The present invention relates to a fixing device and an image forming apparatus having the fixing device.
As a general fixing device, one composed of a rotor and an endless belt, which form a nip section for fixing an image onto a conveyed sheet, a pressure member which comes into sliding contact with the inner surface of the endless belt, and a heating section for heating either one of the rotor and the endless belt to a fixing temperature is known (See JP 2003-5553 A, JP 2005-4126 A, JP 2004-198695 A, JP 2005-62568 A, and JP H8-137310 A). The pressure member is composed of a holding frame which includes a groove section having a recessed cross section and extending along the width direction of the sheet, and a pressing member housed in the groove section of the holding frame. The pressing member is pressed toward the rotor so that the rotor and the endless belt are put in pressure contact with each other.
Generally, this kind of pressure member suffers displacement of the pressing member during assembling operation for housing the fixed pressing member into the holding frame as well as during operation for solving such problem as sheet jam. Accordingly, it has been known, as shown in FIG. 7A, that the displacement of the pressing member with respect to a conveyance direction of a sheet (referred to as “pressure pad position moving amount” in the horizontal axis of FIG. 7A) changes a ratio of the conveyance speed of both end sections of the sheet to the conveyance speed of a central section of the sheet (referred to as “paper sheet conveyance speed ratio” in the vertical axis of FIG. 7A). When the conveyance speed ratio is 0.2% or more, paper wrinkling tends to occur. It is also known, as shown in FIG. 7B, that change in pressure pad position moving amount changes the nip width, which may deteriorate the fixing quality of the fixing operation (symbol □ in FIG. 7B shows variation of the central section and symbol ⋄ shows variation of the drive side).